(1) Field of the Invention
The present invention relates to a time managing apparatus that manages times clocked by a plurality of apparatuses on a network, and specifically to a technique for synchronizing a plurality of apparatuses in terms of the time or execution of an event.
(2) Description of the Related Art
FIG. 31 shows a conventional network structure, where a plurality of apparatuses are connected to the network. As shown in FIG. 31, a set-top box (STB) 91, a personal computer (PC) 92 being a controller, a tuner 93, and a video tape recorder (VTR) 94 being a target apparatus are connected to a network 95 so that they can communicate with each other.
The PC 92 can synchronize in terms of the time with an internet broadcasting station 96 by communicating with it. The tuner 93 can synchronize in terms of the time with a broadcasting station 97 by receiving broadcasting data from it.
Each controller can control the target apparatuses.
Suppose the user presets a recording of a TV program using the PC 92. When the preset start time is reached, the PC 92 transmits a Play command to the tuner 93 to start receiving the TV program, and at the same time, the PC 92 transmits a Rec command to the VTR 94 to start recording the received TV program. When the preset stop time is reached, the PC 92 transmits a Stop command to the tuner 93 and the VTR 94 to stop the operations.
Here, each of the above apparatuses has a time managing unit and clocks the time separately. For this reason, when a plurality of apparatuses try to execute a certain event simultaneously, the start time or the stop time may be different for each apparatus.
This may cause the following problem, for example. Suppose the time clocked by the PC 92 is delayed from the tuner 93 that is synchronizing with the broadcasting station 97, and that the PC 92 is preset to record a TV program that is broadcast by the broadcasting station 97 and received via the tuner 93. Then when the PC 92 starts recording the preset TV program, the broadcasting station 97 has already started broadcasting the TV program, and the PC 92 fails to record the first part of the TV program.